1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission which can be used as a transmission for a vehicle and, in particular, to an improvement in a retainer of a loading cam device which is incorporated into such toroidal-type continuously variable transmission.
2. Description of the Related Art
Now, FIG. 4 shows a conventional toroidal-type continuously variable transmission which can be used as a transmission for a vehicle. This is a so called double cavity type of toroidal-type continuously variable transmission for high torque, in which two input side disks 2, 2 and two output side disks 3, 3 are mounted on the outer periphery of an input shaft 1. Also, on the outer periphery of the middle portion of the input shaft 1, there is rotatably supported an output gear 4. The output gear 4 includes cylindrical-shaped flange portions 4a, 4a formed in the central portion thereof, while the output side disks 3, 3 are respectively coupled to the flange portions 4a, 4a of the output gear 4 through spline engagement.
Also, the input shaft 1 can be driven or rotated through a loading cam device 12 by a drive shaft 22. Specifically, the loading cam device 12 is interposed between the input shaft 1 and the input side disk 2 that is situated on the left in FIG. 4; and, while pressing the input side disk 2 elastically toward the output side disk 4, the loading cam device 12 can drive and rotate the input side disk 2. The loading cam device 12 is composed of a loading cam (cam plate) 12a rotatable together with the input shaft 1 and a plurality of (for example, three) rollers (rolling elements) 12b respectively held by the retainer 7 in such a manner that they are allowed to roll. In one side surface (in FIG. 4, the right side surface) of the loading cam 12a, there is formed a cam surface 113 consisting of an uneven surface (convex-and-concave surface) which extends in the circumferential direction of the loading cam 12a; and, in the outer surface (in FIG. 4, the left side surface) of the input side disk 2 as well, there is formed a cam surface 114 having a similar shape to the cam surface 113. By the way, the output gear 4 is supported on the interior of a housing 14 through a partition wall 13 which is constructed by coupling two members to each other, whereby the output gear 4 can be rotated about the axis O of the input shaft 1 but is prevented from shifting in the axis O direction.
The output side disks 3, 3 are supported by needle roller bearings 5, 5 interposed between the input shaft 1 and the output side disks 3, 3 in such a manner that they can be rotated about the axis O of the input shaft 1. Also, the input side disks 2, 2 are supported through ball splines 6, 6 on the two end portions of the input shaft 1 in such a manner that they can be rotated together with the input shaft 1. Further, between the inner surfaces (concave surfaces) 2a, 2a of the input side disks 2, 2 and the inner surfaces (concave surfaces) 3a, 3a of the output side disks 3, 3, there are rotatably interposed and held power rollers 11, respectively.
In the case of the input side disk 2 that is situated on the right side in FIG. 4, the back surface (in FIG. 4, the right surface) of the input side disk 2 is butted against a loading nut 9 through a countersunk plate spring 10 having large elasticity and thus the shift of the present input side disk 2 with respect to the input shaft 1 in the axial direction thereof (in FIG. 4, in the right and left direction) is substantially prevented. In the end portion of the input shaft 1, there is formed a flange portion 1a; and, in one side surface of the flange portion 1a, there is formed an angular type of inner raceway 62. And, between this inner raceway 62 and an angular type of outer raceway 64 formed in the inner peripheral surface of a bearing support member (outer ring) 63, there are inserted a plurality of balls 65. That is, the flange portion 1a, bearing support member 63 and balls 65 cooperate together in constituting an angular contact type of ball bearing 66 which is capable of supporting a thrust load.
In the outer peripheral surface of the bearing support member 63, there are formed a cylindrical surface 67 and a flange portion 53. And, in order that a cylindrical portion 56 formed in the diameter-direction middle portion of the loading cam 12a can be fitted with the outer surface of the cylindrical surface 67 with no shaky motion between them and shiftably in the axial direction of the loading cam 12a, a countersunk plate spring 57 for prevention of shaky motion is interposed between the flange portion 53 and the outer surface of the middle portion of the loading cam 12a. 
Also, between the diameter-direction inner portion of the bearing support member 63 and input side disk 2, there are interposed a thrust needle roller bearing 55 and a countersunk plate spring 42 serving as a preload spring in such a manner that they are arranged in series with each other along the axial direction of the input shaft 1. The countersunk plate spring 42 is smaller in elasticity than the countersunk plate spring 10 and is able to apply a preload to the contact portions between the concave surfaces 2a, 2a, 3a, 3a of the disks 2, 2, 3, 3 and the peripheral surface of the power rollers 11, 11. That is, when the loading cam device 12 does not generate a thrust force, or when a thrust force is generated but it is small, the countersunk plate spring 42 secures the contact pressures of the respective contact portions so that small torque can also be transmitted by the toroidal-type continuously variable transmission.
Therefore, in the case of the above-structured continuously variable transmission apparatus, in case where rotational power is input to the input shaft 1 from the drive shaft 22, as the input shaft 1 is rotated, the loading cam 12a is rotated, the cam surface 113 presses the plurality of rollers 12b against the cam surface 114 formed in the outer surface of the input side disk 2. Due to this, the input side disk 2 is pressed against the plurality of power rollers 11 and, at the same time, based on the mutual pressing actions between the two cam surfaces 113, 114 and the plurality of rollers 12b, the input side disk 2 is rotated. And, the rotational power of the input side disk 2 is transmitted through the plurality of power rollers 11, 11 to the output side disk 4 with a given transmission ratio. Also, the rotational power of the output side disks 3, 3 is transmitted from the output gear 4 to the output shaft 17 through a transmission gear 15 and a transmission shaft 16.
By the way, the retainer of the loading cam device 12 in the above-structured toroidal-type continuously variable transmission, as shown in FIGS. 5A and 5B, comprises a retainer main body 7a which is made of a metal plate having a circular-ring-like shape. Also, the retainer main body 7a includes in the central portion thereof a circular-shaped fitting hole 30 which can be fitted with a boss portion 28 (FIGS. 6A-6C) formed in the loading cam 12a. Also, in the outer peripheral portion of the retainer main body 7a, at regular intervals in the peripheral direction thereof, there are disposed e.g. four projecting portions 31 integrally therewith; and, in the respective projecting portions 31, there are formed pockets 32 respectively for holding their associated rollers 12b. 
Also, as described above, in the case of the loading cam device 12, the uneven surface shape (convex-and-concave surface shape) of the cam surface 113 of the loading cam 12a presses the plurality of rollers 12b against the cam surface 114 of the input side disk 2. As a result of this, the inner peripheral surfaces 2a, 3a of the input side disk 2 and output side disk 3 are strongly pressed against the peripheral surfaces of the power rollers 11. Due to this, the loading cam 12a receives a strong force from the plurality of rollers 12b in the axial direction of the input shaft 1, which raises a problem as to the yield strength of the connecting portion (stepped portion—see FIG. 6A) 28a between the cam surface. 113 and boss 28 on which stresses are concentrated. Therefore, in order to enhance the yield strength of the connecting portion 28a, as shown in FIG. 6B, the connecting portion 28a is formed in an arc shape, or, as shown in FIG. 6C, there is formed an-arc-shaped relief portion 39 in the connecting portion 28a. 
Also, in the loading cam device 12 having such structure, in case where torque is input to the loading cam 12a, the roller 12b climbs the cam surfaces 113, 114, while the distance between the loading cam 12a and input side disk 2 becomes large. Therefore, in order to prevent the retainer 7 from inclining even when the distance becomes large, not only, on the outer peripheral portions of the respective projecting portions 31 of the retainer main body 7a of the retainer 7, there are disposed outside-diameter-side projecting portions 33 which are respectively projected toward the input side disk 2, but also, on the inner peripheral portions of the fitting hole 30 that correspond to the projecting portions 31, there are disposed inside-diameter-side projecting portions 34 which are respectively projected toward the loading cam 12a side. That is, the retainer 7 includes, on the diameter-direction inside and outside surfaces thereof, the projecting portions 33, 34 which can prevent the retainer 7 from toppling down.
Since the projecting portions 33, 34 keep the inclination of the retainer 7 by maintaining the distance between the projecting portions 33, 34 and cam surfaces 113, 114, it is not preferable that the projecting portions 33, 34 drop down into the relief portions 39 formed in the loading cam 12a or they interfere with the arc-shaped connecting portions 28a. However, in case where the connecting portion 28a is formed in an arc shape or the relief portion 39 is formed in the connecting portion 28a in order to enhance the yield strength of the loading cam 12a, there arises a problem that the inside-diameter-side projecting portion 34 can drop down into the relief portion 39 (see FIG. 6C) or the inside-diameter-side projecting portion 34 can interfere with the connecting portion 28a to thereby make it difficult to maintain the attitude of the retainer 7.
As the shape of the retainer 7, conventionally, there are known various shapes (see JP-A-8-200463, JP-A-11-193856, and JP-A-11-63165). However, there has not been proposed yet a retainer having such a shape that can prevent the inside-diameter-side projecting portions 34 from interfering with relief portions 39 or connecting portions 28a. 